This invention relates to a radio-frequency (rf) antenna coupler that permits unobtrusive addition of a Low-Frequency (LF) navigational receiver capability to any platform that has an existing capability installed for receiving any standard broadcast-communications. In recent years, there has been increasing interest for fitting automobiles with GPS capabilities to assist the vehicle operator when driving in situations involving unfamiliar terrain and/or location fixing or identification in emergency scenarios. There is also an increasing demand from various fleet-vehicle companies for systems capable of asset management and vehicle tracking. With the onset of differential techniques applied to GPS usage or DGPS, the accuracy of positional determination has greatly improved and allows better real-time indication of speed, direction of travel and distance traversed. All such improvements are serving to boost interest and enthusiasm for wanting DGPS capability embedded into automobiles and other varieties of vehicular platforms. The most popular choice of DGPS implementation has been towards using radio-beacon methods because of the free access combined with a reasonable area of coverage. The most common usage has been of those systems based on the rf-band 283-kHz to 325-kHz, to utilize the networks and services provided by organizations such as the United States Coast-Guard (USCG). Hitherto the installation of such a radio-beacon receiver has dictated the mounting of a separate specialized antenna specific to the rf-band, which unfortunately proved ineffective for use with the on-board AM/FM radio receiver mounted as standard on most automobiles. Usually the antenna used was a type normally intended for marine applications, so it was invariably quite bulky. Such an additional specialized antenna not only incurred extra cost but was also perceived as being detrimental to the aesthetics of the host automobile; consequently this approach lost public appeal. The bulkiness and rather unusual profiles of these specialized antennae did not allow inconspicuous installations to be achievable.
This invention relates broadly to rf coupling circuits enabling any platform-mounted antenna system and its associated standard broadcast-communications radio receiver, to also be used in conjunction with a navigational receiver. An exemplary embodiment of the invention is an antenna coupler for coupling a broadcast communications antenna with a broadcast communications receiver and a navigation receiver. The coupler includes independent rf paths for coupling the broadcast communications antenna to the broadcast communications receiver and the navigation receiver.